US2877377A - Beam tube switching circuits - Google Patents

Description

March 10, 1959 F. E. ZOGG BEAM TUBE SWITCHING CIRCUITS Filed Jan. 23, 1958,

ISV.

M U LT V IBRATOR uvvsuron FREDERICK E. 2066 A T TOR/VE Y United 2,877,377 BEAM TUBE SWITCHING CIRCUITSI Frederick E. Zogg, Ontario, N. assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application January 23, 1958, Serial No. 710,651 7 Claims. (Cl. 315-21) This invention relates generally to multi-position electron beam switching tubes and to systems for clearing an electron beam from ,a position in the tube and resetting the beam in a selected 0 position.

One type of multi-position electron beam switching tube, to which the principles of the invention'apply, is described in U. S. This type of tube includes a central cathode which is surrounded by a plurality of groups of electrodes, each group representing a position at which an electron beam may be formed. Each group of electrodes includes a target electrode for receiving an electron beam and Patent No. 2,721,955 of Fan et al. v

developing an output signal therefrom, and a spadeelec:

trode adapted to form'and hold an electron, beam on its associated target electrode. Each group of electrodes may also include a switching electrode for switching an electron beam from one group of electrodes to the next under the influence of crossed electric and magnetic fields.

Generally, in the operation of a tube of this type, with all of the tube electrodes carrying their normal supply voltages, electrons emitted by the cathode are retained in the vicinity of the cathode, and an electron beam does not form in any of the tube positions. Whenaspade or switching electrode has its electrical potential suitably reduced, the electric field pattern is altered and an electron beam forms on a target electrode associated with that spade or switching electrode. Ordinarily, the electron beam thus formed may be moved from one position to the next by means of suitable electrical pulses applied to the switching electrodes.

In some applications of these tubes, for example in decade counters or the like, it is desirable to be able to allow the tube to execute a predetermined counting operation, that is, to move from position to position until it reaches a predetermined position and then to clear the tube and reset the electron beam at ,a selected 0 position. Circuits are known for clearing and resetting tubes of the type described'above, and, although these known circuits are generally satisfactory, they are characterized by comparatively low speed of operation.

Accordingly, one object of the present invention is to provide an improved circuit for clearing and resetting an electron beam in a multiposition electron tube. 1

Another object ofv the invention is to provide an improved high speed circuit for clearing and resetting an electronbeam in a multi-position electron tube.

.The present invention is particularly applicable to the 2,877,377 Patented Mar. I ll), 19 59 ice 2 electrode. This operation clears the tube of an electron beam which might have been flowing to one 'of the target electrodes. Subsequently, the potentials of the spade buss and the spade electrodes are allowed to rise rapidly toward their normal operating levels. However, the potential of the spade electrode at the selected. 0 position, at which it is desired to re-set or re-form the electron beam, rises slowly so that this 0 spade carries a lower electrical potential than the other spades and the electron beam forms at the 0 position. i

The invention is described in greater detail by reference to the single sheet of drawings wherein:

Fig. l is a perspective view of an electron beam switching tube of a type with which the principles of the invention maybe employed; and

Fig. 2 is a schematic representation of the tube of Fig. 1 and a circuit in which it may be operated.

The invention is described below as it applies to a multi-position electron beam tube of the type shown in U. S. Patent No. 2,721,955 to vFan et al. This type of tube 10 is shown in Fig. 1 and includes, briefly, an envelope '12 which contains a central longitudinally elongated cathode 14 and ten groups of electrodes spaced radially from the cathode and surrounding the cathode. Each group of electrodes includes a generally U-shaped elognated spade electrode 16 and a target electrode 18 positioned so that each target occupies the space between adjacent spade'electrodes. Each spade electrode serves to form and hold an electron beam on its associated target electrode. A generally rod-like switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. An open-ended cylindrical permanent magnet 22 is provided surrounding the tube envelope and coaxial therewith. The magnet provides an axial magnetic field which is utilized in conjunction'with electric fields within the tube to form and switch an electron beam from the cathode to each of the groups of electrodes.

Briefly, in operation of tube 10, electrons emitted by the cathode are retained at the cathode if each of the spades, targets and switching electrodes carries its normal operating electrical potential. When a spade or switching electrode experiences an appropriate reduction in potential, an electron beamis formed and directed to a target electrode. The electron beam is switched from one target electrode to the next by thus suitably altering the electrical potentials of a spade or switching electrode.

A circuit embodying the invention is shown in Fig. 2 wherein the tube 10 is shown schematically in linear form. To simplify the drawing, only three of the usual ten positions or groups of electrodes, numbered 0," 1, and 9, are shown. In the circuit, the cathode 14 is connected to a source of reference potential such as ground. Each spade electrode 16 is connected through a spade load resistor 26 to a common spade buss 28. The spade buss 28, in turn, is coupled through a common spade load resistor 30 to a positive supply voltage of about 200 volts. This arrangement provides a bias voltage of about volts on the spade buss. Each target electrode 18 is coupled through a load resistor 38 to a common target buss 40 which is coupled, in turn, to the positive 200 volt supply voltage.

The switching electrodes 20 which are employed to switch an electron beam from position to position within the tube 10 may be connected in any one of a number of suitable ways to provide the desired switching operation. According to one suitable arrangement as shown, the switching electrodes are connected in two sets, with alternate electrodes being connected together to form a set. The two sets of switching electrodes are coupled to a suitable source of switching pulses such position. for generating and applying a negative pulse to the spade buss and thus to all of the spades, an operation which- 1 causes the tube to clear; and second operating voltage more l other positions. This operation of the spade causes 3 it to earry,iforasuitable length of:time, the lowest electrical potential ot'all of the spades, and, as a result, an electron beam forms at the 0 position.

spade buss capacitor '70 to ground.

beam from one position to the next. y

Accoi-dingto the invention, circuit means are provided for clearing andresetting an electron beamat a desired position within the tubelll. For.purposes'ofillustrabe considered the Zero, or reset, the circuit comprises first means of the positions may Essentially,

the spade. at the 0*? position to return to its normal ay be employed ZOne suitable cir- Any suitable pulse generator circuit for the above-mentioned first means;

cuit employs a thyratron 44, for example'a type 5696 thyratron, which includes a cathode 46, a control grid 48, a shield grid 50, of the thyratron is connected to ground, a'nd'tfhe'control grid 48 is coupled through-a suitable biasresistor54 to a negative bias voltage of the order of 115 volts: The control; grid is also coupled through a capacitor 56 to a suitable source of positive pulses 58. v The shield grid 50 V is connected to the cathode, and the: anodefilis' coupledthrough a load resistor 60 to the target buss 40 and'the 200. volt supply; 'The anodes; is also coupled to the through a differentiating. network which includes a capacitor 62 and resistorfit) conneeted'in series I between the 'thyratron' anode and the target. buss with means for causing slowly. than the spades at, theand an. anodeSZ. The cathode 46 don, the circuit shown is adapted to clear'the tube and reset the. beam at the zeroposition. Of. course, any one 0"position'is thus maintained at alower potential than the other spades for a period of timc,,the electron beam- -from the cathode forms on the target at the 0, position under the influence'ofthespade at. this position,

In one typical circuit, the target resistors 38 have a value of. about 18,000 ohms; the spade resistors 26 have a valueof about 100,000- ohms;. and the capacitor 74 has a value of about 100' urf. The pulses '32 have-a,

-magni tude of aboutQ-IOG volts and a rise" time of ap' proximately use'c. minimum from a low impedance source; The spade supply voltage is about 150'volts,

andthe target supply voltage is about 200 volts.

and a plurality'of groups of electrodes arrayed in: elec tron beam receiving relation with respect to said cathode; each of said groupsof electrodes including an electron beain'target electrode and :a spade electrode adapted to form and hold an electron beam on its associated target, I

What is'claimed is:

l. An electron beam clearing and resetting circuit for a multi-position electron beam tube comprising an electron beam tube including an electron emitting cathode electrode; a common spade- .buss', .a. spade impedance coupled between each of said, spade electrodes common spade: buss; spade. buss'for' changing the potential ofthe buss and potential and a lower potential; and

I for raising the-potential thereof from said lower potens the junction 64 between them being connected to:tl1c:

spade buss. The junction'disalso coupled through a mentioned, includes at the 0" spade, a'diode 72 which is connected across the 0 spade load resistor 26 with its anode connected to the spade and its cathode con nccted to the spade buss. The diode 72 is thus oriented to provide easy current flow from the boss to the spade. The 0" spade and the anode of the diode are also connected through a capacitor 74 to ground.

In operation of the circuit of Fig. 1, let it be assumed that the tube is counting in normal fashion and an electron beam is being switchcd from position to position under the influence of pulses applied to the switching electrodes from the multivibrator 42. When it is desired to clear and reset the tube, a positive pulse 58 is applied to the thyratron 44- which fires and produces a negative pulse 76 at the spade buss 28. The negative pulse 74 has an amplitude slightly larger than 100 volts and lowers the spade buss and the spade electrodes in potential to 0 volt or below. The diode 72 serves to rapidly discharge capacitor 74 to the potential of spade buss 28. Capacitor 74 had previously been charged to the potential of the spade buss. Since all of the spade electrodes are at the same potential, the electron beam is cleared from the position in which it was formed and electrons are held in the vicinity of the cathode under the influence of the crossed electric and magnetic fields in the tube. After the pulse 76 has passed, the spade buss returns to its normal operating level of about 100 volts with respect to cathode l4, and all of the spade electrodes return to their normal operating voltages of about 100 volts except the spade in the "0 position. This 0 spade is maintained initially a reduced voltage of about 0 volt by the discharged capacitor "1'4, and the rate at which this spade returns to normal operating voltage is determined by the time constant of the network including spade resistor in parallel with the reverse resistance of the diode 72 and capacitor 74. Since the spade at the tial to said reference potential at a'slower. rate than the other of said spade electrodes sothat, potential of saidselected spade is lower than: the potcntials of the other spades and. an electron beam forms on the target electrode associated with said selected spade electrode.

2 A circuit defined ,3. A beam clearing andresetting circuit foran elecs tron beam switchingidevice-comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a spade impedance coupled between each of said spade electrodes and a common spade buss; circuit means connected to said spade buss for changing the potential thereof at a certain rate between a positive operating potential and a lower reference potential; and circuit means coupled to said selected spade electrode for raising the potential thereof from said reference potential to said operating potential at a slower rate than the other of said spade electrodes so that momentarily said selected spade is at a lower potential than the other spades and an electron beam forms on the target electrode associated with said selected spade electrode.

4. The circuit defined in claim 3 wherein said circuit means includes a capacitor coupled between a source of reference potential less positive than said operating and reference potentials and the spade impedance of said selected spade electrode, and a diode connected across said last-named spade impedance.

5. The circuit defined in claim 3 wherein said circuit means comprises a crystal diode connected between the spade impedance of said selected spade electrode and a source of reference potential lower than said operating potential and said lower reference potential.

6. A beam clearing and resetting circuit for an electronic switching device comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam and said i circuit means connected to said predeterminedrate between a for a time, the

p in claim wherein said circuit. means includes a capacitor andadiode, said diode being connected across thespade resistoroi said selectedspade. t

target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a spade buss; means for applying a positive operating potential to said spade buss and to said spades; a spade impedance coupled between each of said spade electrodes and said common spade buss; a source of negative voltage pulses coupled to said spade buss for applying negative pulses to said spade buss and thereby lowering the potential of said buss and said spade electrodes from said operating potential to a lower reference potential; and means for raising the potential of said selected spade electrode from the lower reference potential to said operating potential at a slower rate than the other of said spade electrodes when a negative pulse is not present at said spade buss so that said selected spade electrode is momentarily at least at a lower potential than the other of said spade electrodes and an electron beam forms on the target electrode associated with said selected spade electrode.

7. A beam clearing and resetting circuit for an elec- 29 tron beam switching device comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode; each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss to which each of said spades is connected; separate sources of high and low reference potentials coupled to said spade buss; and time delay means coupled to a selected one of said spades for raising said selected spade from said low reference potential to said high reference potential at a slower rate than the other of said spade electrodes are raised so that said selected spade has at least momentarily a lower potential than the other spades and an electron beam forms on the target electrode associated with said selected spade electrode.

No references cited.

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